This invention relates to a new antibiotic complex, designated CP-55,358, and more particularly to the two major antibiotics contained therein, designated CP-56,063 and CP-56,064. The complex was derived from fermentation of a new Streptomyces culture, designated culture N409-40, obtained from a soil sample in India. Chemically, the two major antibiotics are macrolide compounds, having 16 members in the lactone ring. However, they both differ from known 16-membered macrolides, e.g. tylosin, in that they have a previously-unknown sugar unit attached to the C-5 position.